GB2151157A

GB2151157A - Dielectric sheet material

Info

Publication number: GB2151157A
Application number: GB08430828A
Authority: GB
Inventors: Norman Reginald Gilbert Crook; John William Manning
Original assignee: BENSON ELECTRONICS
Current assignee: BENSON ELECTRONICS
Priority date: 1983-12-06
Filing date: 1984-12-06
Publication date: 1985-07-17
Also published as: EP0145463A2; GB8430828D0; GB2151157B; EP0145463A3; CA1263554A; JPS60185954A; GB8332547D0

Abstract

A dielectric sheet material for use on electrographic machines comprises a base sheet having a first coating of a cationic conductive polymer and a second coating overlying the first coating of a polymeric material with affinity for an electrostatic printing toner.

Description

1 GB 2 151 157 A 1

SPECIFICATION Dielectric Sheet Material

This invention relates to dielectric sheet materials, which may be in the form of individual sheets, a continuous web or a roll (hereinafter referred to as "sheet materials"), and more especially to such materials for use with electrostatic printerlplotter machines (sometimes referred to as electrographic machines).

In an electrostatic printerlplotter process an image is produced on a dielectric coated sheet material which is normally either a dielectric coated paper or polyester film. The dielectric coated sheet passes over a fixed writing head with conducting styli equally spaced in rows. When a stylus is energised by a computer generated signal it places an electrostatic charge on the paper at the point of stylus contact. A toner is then 10 applied to the sheet material and toner particles adhere to the charged areas so that a permanent, high contrast image is produced.

The dielectric sheet materials currently used with printerlplotter machines are usually polyester films coated with a surface layer providing a greater affinity for the toner than is provided by the polyester itself and having on each a continuous narrow strip of carbon particles. The application of these carbon strips is a 15 costly operation and consequently carbon edged dielectric printing films are extremely expensive materials.

This invention provides a dielectric sheet material for use with electrostatic printerlplotter machines which does not have carbon strips on its two longitudinal edges.

According to the invention a dielectric sheet material comprises a base sheet or film having a first 20 coating of a cationic conductive polymer and a second coating of a polymeric material with affinity for an electrostatic printing toner.

The base sheet or film may be of any material and may be transparent, translucent or opaque and may be either wholly or partially through-conductive or non-conductive.

The top coating may cover the whole area of the coating of cationic polymeric polymer or, especially when the base sheet is non-conductive there may be left a longitudinal edge strip of uncoated cationic polymer on one or both sides of the sheet material.

As non-conductive base materials there may be mentioned, for example, polyethylene terephthalate (polyester) film or nylon film. Polyolefin films may be mentioned as an example of partially through- conductive materials. As through-conductive materials there may be mentioned, for example, paper and 30 the various synthetic paper-like materials produced, for example, by biaxialiy orienting and at least partially whitening such materials as pofyolefins, for example, polyethylene and polypropy(ene. Ad an example of such a paper-Uke material there may be mentioned the materials sold under the trade marks Synteape, Yupo and Polyart.

As the cationic conductive polymers for use in the process there may be mentioned quaternary 35 nitrogen containing salts of polymers such as, for example, polyvinyl benzy] trimethyl ammonium chloride, polydiallyl dimethyl ammonium chloride, poly(2-methacryloyloxy ethyl trimethyl ammonium chloride), poly(Wacrylamide propyl-3-tri methyl ammonium chloride), poly(N,N- dimethyi-3,5-methylene piperidinium chloride, poly 4-vinyl-N methyl pyridi niu m chloride, quaternised polyethyleneimine and the tri-methylamine derivative of polyepichlorhydrin.

The conductive polymer is preferably applied from aqueous solution which may contain a minor amount of organic solvent.

The thickness of the coating applied should be sufficient to give a continuous uniform coating on the surface and preferably to flatten any surface irregularities, for example, such as those produced by fibers projecting from the surface of paper. Moreoverthe coating must be such as to allow the production of a 45 uniform charge over the entire coated surface of the sheet. Preferably, the amount of polymer applied in the conductive coating is within the range of 0.8 to 2.5 gram per square metre. Similarly the thickness of the top coating should be such as to give a continuous uniform coating over the surface of the conductive coating.

Preferably, the amount of polymer applied in the top coating is within the range of 4 to 10 gram per square metre.

The top coating may be produced from any soluble film-forming polymeric material which affords an affinity to the toner particles, and may be, for example, a vinyl acetate copolymer, a polyvinylbutyral, a styrene polymer or copolymer or a thermoplastic polyester or mixtures of any two or more thereof.

Preferably, the top coating is a coating of a soluble linear thermoplastic copoiyester, preferably a copoiyester from polybasic aromatic acids and aliphatic polyhydroxy compound(s).

Advantageously, the top coating polymer has a surface resistivity of from 100 to 5000 megohm per square at 20% relative humidity and from 5 to 150 megohm per square at 50% relative humidity, a charge acceptance using a 50OV corona bar between 200 and 490V and a charge decay rate of 6 to 20V per second.

These polymers may be applied from solution in organic solvents or mixtures of solvents such as, for example, methylethyl ketone toluene or ethanol. The polymers may be used in admixture with a minor 60 proportion of other resins and may be used in conjunction with small amounts of fillers, for example, silica fillers.

The conductive and top coating may be applied by any desired technique, for example, an air-knife Meyer rod, roller, trailing blade, or Gravure technique.

2 GB 2 151 157 A 2 It will be seen that the invention provides inter alia a dielectric sheet for use with printerlplotter machines which is based on polypropylene. It has not previously been possible to produce electrostatic images in such materials. Since paper-like polypropylene sheet is cheaper than polyester film and especially very much cheaper than carbon edged polyester film and moreover is available as translucent or 5 opaque sheet, this represents a considerable advance in the art.

Moreover, according to the invention it becomes possible to produce images on synthetic materials using printerlplotter designed for use with paper only.

The following examples illustrate the invention:- Conductive and top coating formulations were made up as follows:

Conductive Coating (1) Water Polyvinyl benzyltri methyl Ammonium Chloride Conductive Coating (2) Water Polydiallyldimethyl Ammonium Chloride Conductive Coating (3) Water Polydia i lyl di methyl Ammonium Chloride Silica Top Coating (1) Partially hydrolised polyvinyl acetate (20% vinyl alcohol) Toluene Ethanol Silica Top Coating (2) Thermoplastic polyester (Dynapol 206) Toluene Ethanol Silica Top Coating (3) Polystyrene (Picolastic A 75) Polyvinyl butyral (Monsanto Butivar B 72.MW ca 200000) Silica Toluene Methyl Ethyl Ketone parts by weight parts by weight parts by weight 5 parts by weight 94 parts by weight 5 parts by weight 1 part by weight parts by weight 40 parts by weight 25 parts by weight 5 parts by weight parts by weight 40 parts by weight 25 parts by weight 5 parts by weight parts by weight parts by weight 5 parts by weight 50 parts by weight 15 parts by weight 3 GB 2 151 157 A 3 Top Coating (4) Polystyrene (Picolastic A 75) Thermoplastic copolyester (Dynapol 206) 1 parts by weight parts by weight Silica 3 parts by weight Methyl Ethyl Ketone 67 parts by weight Top Coating (5) Soluble vinyl chloridelvinyl acetate/ vinyl alcohol copolymer (Bakelite VAGH) 30 parts by weight Silica 3 parts by weight Toluene 40 parts by weight 10 Methyl Ethyl Ketone 27 parts by weight Cationic coating compositions 1, 2 and 3 were coated onto polyethylene terephthalate film, polypropylene film and the synthetic paper-like material Polyart 11 using an air-knife coating technique in an amount of 1.5 grams per square metre. After the conductive coating had dried one of top coating formulations 1 to 5 was applied to each coated sample using an air-knife in an amount of 7.5 grams per is square metre. In each case, a dielectric sheet material with properties making it eminently suitable for use in electrographic machines was obtained.

Claims

1. A dielectric sheet material comprising a base sheet or film having a first coating of a cationic conductive polymer and a second coating of a polymeric material with affinity for an electrostatic printing 20 toner.

2. A dielectric sheet material according to claim 1, wherein the first coating is a coating of a polymer containing quaternary nitrogen atoms.

3. A process according to claim 2, wherein the first coating is a coating of polyvinyl benzyl trimethyl ammonium chloride, polydiallyl dimethyl ammonium chloride, poly(2- methacryloyloxy ethyl trimethyl ammonium chloride), poly(Wacrylamide propyl-3-trimethyl ammonium chloride), poly(N,N-dimethyi-3,5 methylpiperidinium chloride, poly(4-vinyi-N methylpyridinium chloride), quaternised polyethyleneimine or the tri-methylamine derivative of polyepichlorhydrin.

4. A dielectric sheet material according to any one of claims 1 to 3, wherein the thickness of the coating is sufficient to give a continuous film on the surface and to allow the production of a uniform charge over 30 the entire coated surface of the base sheet.

5. A dielectric sheet material according to any one of claims 1 to 4, wherein the second coating is a coating of a soluble ffirn-forming polymer.

6. A dielectric sheet material according to claim 6, wherein the second coating is a coating of a vinylacetate copolymer, a polyvinyl butyral, a styrene polymer or copolymer or a thermoplastic polyester. 35

7. A dielectric sheet material according to claim 6, wherein the second coating is a coating of a linear thermoplastic copolyester from poly basic aromatic acid(s) and aliphatic polyhydroxy compound(s).

8. A dielectric sheet material according to any one of claims 1 to 7, wherein the base sheet or film is wholly or partially non-conductive and the second coating does not coverthe complete area of the first coating, there being left a longitudinal edge band of uncovered cationic conductive polymer on at least one 40 edge of the sheet or film.

9. A dielectric sheet material according to claim 8, wherein the base sheet or film is of polyethylene terephthalate, nylon or polyolefin.

10. A dielectric sheet material according to any one of claims 1 to 9, wherein the base sheet orfilm is through-conductive and the second coating covers the complete area of the underlying coating of cationic 45 conductive polymer.

11. A dielectric sheet material according to claim 10, wherein the through-conductive base material is paper or a synthetic paper-like material.

12. A dielectric sheet material according to claim 11, wherein the base material is a synthetic paper-like material produced by biaxial ly orientating and stress whitening polypropylene or polyethylene.

13. A dielectric sheet material according to claim 1, substantially as described in the Example.

Printed for Her Majesty's Stationery Office by Courier Press, Leamington Spa. 711985. Demand No. 8817443. Published by the Patent Office, 25 Southampton Buildings, London, WC2A lAY, from which copies may be obtained.